Generally, a digital camera or camcorder uses CCD (Charge Coupled Device) image sensors or CMOS image devices, instead of a film. The CCD image sensors include photosensitive elements and a color filter array provided on the photosensitive elements. The photosensitive elements detect only luminance of a captured image. So, the color filter array has to be provided on the photosensitive elements to obtain luminance and color values to represent the captured image.
There are largely two kinds of color filters. One is a primary-color filter including the RGB color filter, and the other is a complementary-color filter including the CMYG color filter.
A CMYG color filter array accurately detects color of the captured image more accurately than a RGB color array. So, the CMYG color filter array is in wide use for the camcorder.
A DSP (digital signal processor) board in image-processing apparatus for CCTV (Closed-circuit television) performs digital image processing, including color interpolation, gamma correction, automatic exposure and automatic white balance, on the image captured by a CCD camera. After the image processing is done, the captured image is reproduced on a screen.
The CCD camera in the image-processing apparatus includes the CCD image sensors having the CMYG color array which is available for the NTSC/PAL (National Television System Committee/Phase Alternating Line) system. An analog image signal output from the CCD image sensors is converted into a digital image signal by an A/D convertor.
As shown in FIG. 2, Cy, Ye, Mg, and G values obtained from the CMYG color filter array are stored in pixels in the capture image. The Cy, Ye, Mg, and G values are output as a signal in an interlaced scanning way of transferring the odd-numbered lines of the pixels in the captured image, followed by the even-numbered lines of the pixels in the captured image
Modules of the DSP board are shown in FIG. 3, which perform digital image processing on the captured image.
The A/D convertor converts the analog image signal output from the CCD image sensors with the CMYG color array into an (Mg+Cy), (Ye+G), (Mg+Cy), and (Ye+G) signal of 10 bits each. As shown in FIG. 3, the (Mg+Cy), (Ye+G), (Mg+Cy), and (Ye+G) signal of 10 bits each is input into a defective-signal correction unit 1. The defective-signal correction unit 1 corrects a defective (Mg+Cy), (Ye+G), (Mg+Cy), and (Ye+G) signal. Thereafter, a luminance processing unit 2 and a color processing unit 3 extract a luminance Y signal and a Cb and Cr signal from the (Mg+Cy), (Ye+G), (Mg+Cy), and (Ye+G) signal, respectively. Thereafter, gamma-correction units 4 and 5 perform gamma-correction processing on the luminance Y signal and the Cb and Cr signal which are output from the luminance processing unit 2 and the color processing unit 3. Thereafter, an encoding unit 6 encodes the luminance Y signal and the Cb and Cr signal in the NTSC/PAL format. Last, a DAC converts the encoded signal into an analog signal.
A timing signal generation unit 8 generates a driving signal of adjusting a timing of an electric shutter, depending upon amplitude of the luminance Y signal. The driving signal is sent to the CCD image sensors. An interface unit 9 has an inter-integrated circuit for outside connection.
An AE/AWB adjustment unit 7 adjusts automatic exposure (AE) for luminance and automatic white balance (AWB) for color, using the Cb and Cr signal.
The automatic white balance is adjusted by changing the Cb and Cr values. In a conventional method, the Cb and Cr value has to be set to 128, when each of the Cb and Cr signal is in 8 bits. That is, the automatic white balance is properly adjusted by increasing the Cb and Cr value when it is less than 128, and by decreasing the Cb and Cr value when it is greater than 128.
The automatic exposure is adjusted by changing the luminance Y value. That is, the automatic exposure is adjusted by making the luminance Y value closer to a target value.